Partly aromatic copolyamide of reduced triamine content

ABSTRACT

Partly aromatic copolyamides contain as essential components 
     A) 40-90% by weight of units derived from terephthalic acid and hexamethylenediamine, 
     B) 0-50% by weight of units derived from ε-caprolactam and 
     C) 0-60% by weight of units derived from adipic acid and hexamethylenediamine, 
     the components B) and/or C) accounting for a total of not less than 10% by weight of the total units and the copolyamide having a triamine content of less than 0.5% by weight.

This application is a continuation of application Ser. No. 213,624,filed on June 30, 1988, now abandoned.

The present invention relates to partly aromatic copolyamides containingas essential components

A) 40-90% by weight of units derived from terephthalic acid andhexamethylenediamine,

B) 0-50 % by weight of units derived from ε-caprolactam and

C) 0-60% by weight of units derived from adipic acid andhexamethylenediamine,

the components B) and/or C) accounting for a total of not less than 10%by weight of the total units and the copolyamides having a triaminecontent of less than 0.5% by weight.

The present invention furthermore relates to the use of such partlyaromatic copolyamides for producing fibers, films and moldings, and tomoldings obtainable from the partly aromatic copolyamides as essentialcomponents.

Polyamides, such as poly-ε-caprolactam and polyhexamethyleneadipamide,are among the long known industrial plastics and have many areas of use.They are distinguished in general by a high degree of hardness, rigidityand good heat distortion resistance, and are in addition resistant toabrasion and wear and to many chemicals.

For some uses, however, it would be desirable if the heat distortionresistance of the polyamides could be further improved, without theremaining mechanical properties being adversely affected.

These requirements are fulfilled by some copolyamides in which a portionof the aliphatic units are replaced by aromatic units, for examplecopolyamides of adipic acid, terephthalic acid, hexamethylenediamine andε-caprolactam in any combination.

German Patent 929,151 describes a process for preparing highly polymericlinear polyamides, according to which a mixture of an aromaticpara-dicarboxylic acid or an amide-forming derivative thereof, anequivalent amount of an aliphatic or cycloaliphatic diamine and anotherpolyamide-forming starting material, such as a lactam, is condensedunder polyamide-forming conditions. According to the examples thepreparation of the products takes place in a conventional manner in anauto-clave, which, when using terephthalic acid in the momomer mixture,leads to increased formation of triamines from the hexamethylenediaminealso present, which causes strong crosslinking of the product andsubstantially adversely affects the application properties thereof.

British Patent 1,114,541 describes ternary copolyamides which contain,in addition to a major proportion of polyhexamethyleneadipamide, 20-40%by weight of units derived from terephthalic acid andhexamethylenediamine and 2-20% by weight of a further polyamidecomponent. The improvement in the heat distortion resistance of theseproducts compared with conventional polyhexamethyleneadipamides is onlyslight, due to the relatively small proportion of a maximum of 40% byweight of units of terephthalic acid and hexamethylenediamine.

German Laid-Open Application DOS 1,669,455 describes a process forpreparing drawn polyamide filaments by melt spinning a copolyamide,where the copolyamide contains a maximum of 40% by weight of unitsderived from terephthalic acid and hexamethylenediamine, and thepreparation of this polyamide is carried out in the presence of not lessthan 3 mole % of a monofunctional acidic or basic stabilizer. Like theproducts described in British Patent 1,114,541 the copolyamides listedin German Laid-Open Application DOS 1,669,455 also have heat distortionresistances which are only improved to a slight extent compared withconventional polyamides.

German Laid-Open Application DOS 1,620,997 describes linearfiber-forming amide terpolymers which contain units derived from adipicacid and hexamethylenediamine, from terephthalic acid andhexamethylenediamine and from isophthalic acid and hexamethylenediamine.The incorporation of isophthalic acid in the monomer mixture has theeffect that the improved heat distortion resistance obtained byincorporating terephthalic acid is partly lost again. Accordingly, theproducts described in German Laid-Open Application DOS 1,620,997 arealso recommended for use as reinforcing fibers in vehicle tires, ie. forareas of use where high heat distortion resistance is not required.

German Laid-Open Application DOS 3,407,492 describes a process forpreparing copolyamides from adipic acid, terephthalic acid andhexamethylenediamine where the copolyamide contains from 25 to 48% byweight of units of hexamethyleneterephthalamide and where a 40-70%strength aqueous solution of the monomers is heated to not lower than250° C. in less than 15 minutes and is condensed to give a relativeviscosity of up to 1.5-2.4. The water is then distilled off in one ormore steps and the resulting precondensate is fully condensed in aconventional manner. According to the description and the examples theresidence time of the monomer mixture during the precondensation ispreferably 1-10 minutes, and in the examples residence times of 9.5minutes are given. In the continuous production of the copolyamidesdescribed, however, such residence times of more than 1 minute lead toincreased formation of triamines which again favor crosslinking of theproducts formed, leading to difficulties in the continuous productionprocess and adversely affecting the product properties.

EP-A 129,195 and EP-A 129,196, describe a process for the continuouspreparation of polyamides where aqueous solutions of salts ofdicarboxylic acids and diamines, each of 6-18 carbon atoms, are firstheated to from 250° to 300° C. under superatmospheric pressure withsimultaneous evaporation of water and formation of a prepolymer,prepolymer and vapor are continuously separated, the vapors arerectified and any diamines carried over are recycled, an essentialfeature of the process being that the aqueous salt solutions are heatedunder a superatmospheric pressure of 1-10 bar in the course of aresidence time of not more than 60 seconds, with the proviso, that onemerging from the evaporation zone the degree of conversion is not lessthan 93% and the water content of the prepolymer is not more than 7% byweight. It is explained in the description that this proceduresubstantially reduces triamine formation in the preparation ofconventional polyamides, such as poly-ε-caprolactam andpolyhexamethyleneadipamide, but no indication is given here that thiseffect occurs to a significant degree in the preparation of partlyaromatic copolyamides which contain not less than 40% by weight of unitsderived from terephthalic acid and hexamethylenediamine.

It is an object of the present invention to provide a partly aromaticcopolyamide which has improved heat distortion resistance and goodmechanical properties and which can also be prepared continuously in asimple manner without problems due to crosslinking.

We have found that this object is achieved, according to the invention,with the partly aromatic copolyamide defined at the outset.

The partly aromatic copolyamides according to the invention contain ascomponent A) 40-90% by weight of units derived from terephthalic acidand hexamethylenediamine. A small proportion of terephthalic acid,preferably not more than 10% by weight of the total amount of aromaticdicarboxylic acids used, can be replaced by isophthalic acid or otheraromatic dicarboxylic acids, preferably those where the carboxyl groupsare in the paraposition.

In addition to the units derived from terephthalic acid andhexamethylenediamine, the copolyamides according to the inventioncontain units derived from ε-caprolactam and/or from adipic acid andhexamethylenediamine.

The proportion of units derived from ε-caprolactam is not more than 50%by weight, preferably 20-50% by weight, in particular 25-40% by weight,and the proportion of units derived from adipic acid andhexamethylenediamine is up to 60% by weight, preferably 30-60% byweight, in particular 35-55% by weight.

The copolyamide according to the invention may also contain not onlyunits of ε-caprolactam but also units of adipic acid andhexamethylenediamine; in this case, care must be taken to ensure thatthe proportion of units which are free of aromatic groups is not lessthan 10% by weight, preferably not less than 20% by weight. The ratio ofunits derived from ε-caprolactam and from adipic acid andhexamethylenediamine is not subject to any particular limitations here.

Those copolyamides whose composition lies within the pentagon determinedby the corner points X₁ to X₅ in a ternary diagram are preferred, thepoints X₁ to X₅ being defined as follows:

X₁

40% by weight of units A)

60% by weight of units C)

X₂

60% by weight of units A)

40% by weight of units C)

X₃

80% by weight of units A)

5% by weight of units B)

15% by weight of units C)

X₄

80% by weight of units A)

20% by weight of units B)

X₅

50% by weight of units A)

50% by weight of units B)

The figure shows the pentagon defined by these points in a ternarydiagram.

Polyamides containing 50-80% by weight, in particular 60-75% by weight,of units derived from terephthalic acid and hexamethylenediamine (unitsA)) and 20-50% by weight, preferably 25-40% by weight, of units derivedfrom ε-caprolactam (units B)) have proven particularly advantageous formany purposes.

In addition to the units A) to C) described above the partly aromaticcopolyamides according to the invention can contain minor amounts,preferably not more than 15% by weight, in particular not more than 10%by weight, of further polyamide building blocks as known for otherpolyamides. These building blocks can be derived from dicarboxylic acidsand aliphatic or cycloaliphatic diamines, each of 4-16 carbon atoms, andalso from aminocarboxylic acids or corresponding lactams of 7-12 carbonatoms. Suitable monomers of these types are only suberic acid, azelaicacid, sebacic acid and isophthalic acid, as representatives ofdicarboxylic acids, butane-1,4-diamine, pentane-1,5-diamine, piperazine,4,4'-diaminodicyclohexylmethane, 2,2-(4,4'-diaminodicyclohexyl)propaneand 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane as representatives ofdiamines and capryllactam, enanthlactam, omega-aminoundecanoic acid andlaurolactam as representatives of lactams and aminocarboxylic acids.

An essential feature of the partly aromatic copolyamide according to theinvention is the reduced triamine content of less than 0.5%, preferablyless than 0.3%, by weight.

Partly aromatic copolyamides prepared by prior art processes havetriamine contents above 0.5% by weight, leading to a deterioration inproduct quality and to problems in continuous production. A triaminewhich causes these problems is in particular dihexamethylenetriamine,which is formed from the hexamethylenediamine used in the reaction.

Owing to the lower triamine content the copolymers of the invention, forthe same solution viscosity, have lower melt viscosities compared withproducts of the same composition which have a higher triamine content.This considerably improves both the processability and the productproperties.

The melting points of the partly aromatic copolyamides of the inventionlie within the range of from 260° C. to above 300° C., this high meltingpoint also being associated with a high glass transition temperature ofin general higher than 75, in particular higher than 85° C.

Binary copolyamides based on terephthalic acid, hexamethylenediamine andε-caprolactam and which contain about 70% by weight of units derivedfrom terephthalic acid and hexamethylenediamine have melting points inthe region of 300° C. and a glass transition temperature of higher than110° C.

Binary copolyamides based on terephthalic acid, adipic acid andhexamethylenediamine have, even if the terephthalic acid andhexamethylenediamine units account for only about 55% by weight, meltingpoints of 300° C. and higher, while the glass transition temperature isas high as in the case of binary copolyamides which containε-caprolactam instead of adipic acid or adipicacid/hexamethylenediamine.

As in the case of conventional polyamides, the glass transitiontemperature of the partly aromatic copolyamides according to theinvention decreases on water uptake, for example on storage in the air.In contrast to conventional polyamides in which the glass transitiontemperature generally falls to below 0° C. as a result of water uptake,the novel copolyamides have glass transition temperatures significantlyabove 0° C. even after water uptake (conditioning), which has a verypositive effect on the strength and rigidity under standard conditions,eg. at room temperature.

The preparation of the copolyamides according to the invention can becarried out by the process described in EP-A 129,195 and EP-A 129,196.

According to this process, an aqueous solution of the monomers, ie. inthis case those which form the units A) to C), is heated to 250°-300° C.under superatmospheric pressure with simultaneous evaporation of waterand formation of a prepolymer, prepolymer and vapors are thencontinuously separated, the vapors are rectified and any diamine carriedover is recycled. Finally the prepolymer is fed into a polycondensationzone and polycondensed at from 250° to 300° C. and under asuperatmospheric pressure of 1-10 bar. In this process it is essentialthat the aqueous salt solution be heated under a superatmosphericpressure of 1-10 bar in the course of a residence time of not more than60 seconds, the degree of conversion on emergence from the evaporationzone being advantageously not less than 93% and the water content of theprepolymer being not more than 7% by weight.

The formation of triamines is substantially prevented by using theseshort residence times.

The aqueous solutions used have as a rule a monomer content of 30-70% byweight, in particular 40-65% by weight.

Advantageously, the aqueous salt solution is fed at 50°-100° C.continuously into an evaporation zone where it is heated to 250°-300° C.under a superatmospheric pressure of 1-10 bar, preferably 2-6 bar. It isof course the case that the temperature used lies above the meltingpoint of the particular polyamide to be prepared.

As mentioned above, it is essential that the residence time in theevaporation zone is not more than 60 seconds, preferably 10-55 seconds,in particular 10-40 seconds.

On emergence from the evaporation zone, the conversion is not less than93%, preferably 95-98%, and the water content is preferably within therange of 2-5%, in particular 1-3%, by weight.

The evaporation zone is advantageously designed as a tube bundle.Particular ability is possessed by those tube bundles where thecross-sections of the individual tubes are tubular and slotlike in aperiodically repeating manner.

It has also proven to be of advantage if, before separation of thephases, the mixture of prepolymer and vapor is passed through a tubularmass transfer zone provided with internal fitments which is directlydownstream of the evaporation zone while the temperature and pressureconditions used in the evaporation zone are maintained. The internalfitments, e.g. packing such as Raschig rings or metal rings or inparticular packing made of wire mesh, provide a large surface areathrough which the phases, ie. prepolymer and vapor, are brought intointimate contact. This has the effect of considerably reducing theamount of diamine evolved with the water vapor. As a rule, a residencetime of from 1 to 15 minutes is maintained in the mass transfer zone,which advantageously takes the form of a tube bundle.

The two-phase mixture of vapor and prepolymer emerging from theevaporation zone and/or mass transfer zone is separated. Separationgenerally occurs by itself in avessel due to differences in the physicalproperties; for this reason the lower part of the vessel isadvantageously designed as a polymerization zone. The evolved vaporsconsist essentially of water vapor and diamines evolved during theevaporation of the water. These vapors are passed into a column andrectified, suitable columns being for example packed columns, bubble capcolumns and sieve tray columns having from 5 to 15 theoretical plates.The column is advantageously operated under identical pressureconditions as in the evaporation zone. The diamines present in thevapors are rectified off and recycled into the evaporation zone. It isalso possible to feed the diamines to the subsequent polymerizationzone. The rectified water vapor is removed at the top of the column.

The prepolymer obtained, which according to its degree of conversionconsists essentially of low molecular weight polyamide with or withoutresidual amounts of unconverted salts and as a rule has a relativeviscosity of 1.2-1.7, is fed into a polymerization zone. In this zonethe melt produced is polycondensed at 250°-330° C. in particular270°-310° C., under a superatmospheric pressure of 1-10 bar, inparticular 2-6 bar. Advantageously, the vapors evolved during thisprocess are rectified in the column together with the abovementionedvapors, and a residence time of 5-30 minutes is preferably maintained inthe polycondensation zone. The polyamide obtained in this way, which asa rule has a relative viscosity of 1.2-2.3, is continuously removed fromthe condensation zone.

In a preferred method, the polyamide obtained in this manner is passedin molten form through a discharge zone with simultaneous removal ofresidual water contained in the melt. Suitable discharge zones are forexample devolatization extruders. The melt thus freed from water is thencast to give extrudates which are granulated. The granules produced areadvantageously condensed in the solid phase to the desired viscosity bymeans of superheated steam at a temperature below the melting point,e.g. at 170°-240° C., the steam obtained at the top of the column beingadvantageously used for this purpose.

The relative viscosity, measured in a 1% strength solution (1 g/100 mL)in 96% strength by weight H₂ SO₄ at 23° C., is after the solid phasepostcondensation in general within the range from 2.2 to 5.0, preferablyfrom 2.3 to 4.5.

In another preferred method, the polyamide melt discharged from thepolycondensation zone is passed into a further polycondensation zone andcondensed there with continuous formation of new surfaces at from 285°to 310° C. advantageously under reduced pressure, e.g. of 1-500 mbar,until the desired viscosity is reached. Suitable apparatuses are knownas finishers.

Another process which resembles the above is described in EP-A 129, 196,to which reference is made here concerning further details of theprocess.

The partly aromatic copolyamides according to the invention aredistinguished by very good heat distortion resistance coupled with goodmechanical properties, the high level properties being maintained by thehigh glass transition temperature over a relatively wide temperaturerange even after conditioning.

The novel copolyamides are accordingly suitable for producing fibers,films and molded articles.

EXAMPLES Example 1

An aqueous solution consisting of 35 kg of ε-capro-Lactam, 55 kg ofterephthalic acid, 38.5 kg of hexamethyl-enediamine and 128.5 kg ofwater was transported from a heated storage vessel at about 80° C. bymeans of a metering pump at a rate corresponding to 5 kg of polyamideper hour into a partly horizontal, partly vertical tubular evaporatorwhich was heated by vigorous circulation of a liquid heat transfermedium having a temperature of 295° C. The evaporator was 3 m long andhad a capacity of 180 ml and a heat-transferring surface about 1,300 cm²in size. The residence time in the evaporator was 50 seconds. Themixture of prepolymer and water vapor emerging from the evaporator wasat 290° C. and was separated in a separator into water vapor and melt.The melt remained in the separator for a further 10 minutes and was thendischarged in the form of extrudates by means of a discharge screwhaving an evaporation zone, the extrudates were solidified in a waterbath and then granulated. A pressure of 5 bar was maintained in theseparator and the evaporation zone by means of a pressurizing apparatusarranged downstream of the column. The water vapor separated off in theseparator was passed into a packed column which comprised about 10theoretical plates and into the top of which about 1 l/h of condensedvapor was passed to produce reflux. At the top of the column atemperature of 152° C. became established. The water vapor emergingdownstream of the let-down valve was condensed and contained less than0.05% by weight of hexamethylenediamine and less than 0.1% by weight ofε-caprolactam. The bottom product was an aqueous solution ofhexamethylenediamine containing, based on polyamide produced, 80% byweight of hexamethylenediamine and from 1 to 3% by weight ofε-caprolactam. This solution was added again to the starting saltsolution via a pump before entry into the evaporator.

Downstream of the evaporator the prepolymer had a relative viscosity of1.25, measured in 96% strength by weight sulfuric acid at 20° C., and aconversion, according to end group analysis, of from 93 to 95%. Thebishexamethylenetriamine content was from 0.1 to 0.15% by weight, basedon polyamide.

After emerging from the separator, the polymer melt had a very paleself-color and an extremely low bishexamethylenetriamine content of0.17% and also a relative viscosity of from 1.65 to 1.80.

The product had approximately an equivalent number of carboxyl and aminoend groups.

The extractables content (extraction using methanol) was from 3.1 to3.3% by weight.

In the discharge extruder the melt was then let down to atmosphericpressure and underwent virtually no further condensation during aresidence time of less than 1 minute. The granules obtained werecondensed by continuous solid phase condensation with superheated steamat 195° C. and a residence time of 30 hours to a final viscosity η_(rel)of 2.50. The extractables content was then 0.2% by weight (methanolextract).

EXAMPLE 2

A salt solution consisting of 63 kg of a salt of adipic acid andhexamethylenediamine, 30 kg of terephthalic acid, 21 kg ofhexamethylenediamine and 114 kg of water at about 80° C. was passed inat the top of a vertical evaporator 2 m in length having a capacity of120 cm³ and a heat-transferring area about 860 cm² in size. Theevaporator was heated using a vigorously circulated liquid heat transfermedium at 295° C. The mixture of prepolymer and water vapor emergingfrom the evaporator was at 288° C.

The degree of conversion was 94% and the residence time in theevaporator was about 40 seconds.

The mixture of prepolymer and water vapor obtained in this way was fedinto a mass transfer zone which had been charged with packing and had asurface area of 2 m². The mass transfer zone was configured in such away that no significant thermal reaction occurred and the melt ofprepolymer was brought into intimate contact with the water vapor. Theresidence time in the mass transfer zone was 0.5 minutes.

After passing the mass transfer zone the mixture of prepolymer and watervapor was separated in a separator similarly to the procedure ofExample 1. The rest of the procedure also corresponded to that ofExample 1.

The polyamide obtained in this way contained 0.19% by weight ofbishexamethylenetriamine. The proportion of hexamethylenediamine left inthe bottom product was only from 1 to 2% by weight, based on polyamide.

The extractables content (methanol extract) was from 0.2 to 0.3% byweight.

EXAMPLE 3

A copolyamide consisting of 30% by weight of caprolactam units and 70%by weight of hexamethylenediamine/terephthalate units, (prepared as inExample 1), and having a relative viscosity of 2.42, (measured asdescribed in Example 1), and a melting point of 295° C., (measured bythe DSC method), was spun in a commercially availableextruder/meltspinning apparatus under the following conditions:

throughput: 1.2 kg/hour.

melt temperature: 335° C.

spin speed: 690 m/min.

spinnerette: 20 hole; hole diameter 0.2 mm.

The filament yarns obtained were subsequently hotdrawn:

draw ratio: 1:2.4.

drawing temperature 120° C. (godet) and 140° C. (hot plate).

drawing speed: 735 m/min.

The filament yarns had the following properties:

    ______________________________________                                        total count:      112/20 dtex                                                 tensile strength: 4.65 cN/dtex                                                                             (4.6)                                            elongation at break:                                                                            20%        (36)                                             initial modulus:  60 cN/dtex                                                  ______________________________________                                    

dyeability with anionic dyes: comparable with polyhexamethyleneadipamide(nylon-6,6)

Fastnesses (light, wash, perspiration) comparable with nylon-6,6

    ______________________________________                                        wet strength:         87       (87)                                           UV Stability (Xenotest, 28 days):                                                                   69%      (52%)                                          heat treatment (3 hours at 190° C.):                                                         37%      (40%)                                          ______________________________________                                    

The values given in parentheses are those for nylon-6,6.

We claim:
 1. A partly aromatic copolymide consisting essentially of:(A)50-80% by weight of monomer units derived from terephthalic acid andhexamethylenediamine, and (B) 20-50% by weight of monomer units derivedfrom ε-caprolactam, wherein said copolyamide has a triamine content ofless than 0.3% by weight, a melting point in the range from 260° C. toabove 300° C. and a glass transition temperature higher than 75° C. 2.The copolyamide of claim 1, consisting essentially of:A) 60-75% byweight of monomer units derived from terephthalic acid andhexamethylenediamine, and B) 25-40% by weight of monomer units derivedfrom ε-caprolactam.
 3. A molded article comprising the copolyamide ofclaim
 1. 4. The molded article of claim 3, wherein said molded articleis a film or fiber.